An organopolysiloxane that contains acrylic or methacrylic groups can be combined with an improver of an acryl- or methacryl-type resin in the form of a silicone macromonomer or it can be used as one of the main components of a silicone composition by adding a photosensitizer to form a composition cross-linkable by irradiating with high-energy beams such as UV radiation beams. In Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) H8-73592, an organopolysiloxane that contains an acrylic or methacrylic group on one terminal is disclosed as an organopolysiloxane having acryl- or methacryl-polymerizable groups and obtained by reacting a dimethylmonohalosilane having an acrylic or methacrylic group with a polymer obtained by anion-living polymerization of a hexamethylcyclotrisiloxane by using a low-molecular-weight compound with a siloxylithium on one terminal as a reaction initiator, in the presence of an amine compound. Furthermore, Kokai H9-12724 discloses a diorganopolysiloxane that contains an acrylamide or methacrylamide group on one terminal and is obtained by causing a reaction between a halideacrylate or halidemethacrylate and a diorganopolysiloxane that contains an amino group on one terminal in an alkaline aqueous solution. However, an organopolysiloxane that contains aliphatic, unsaturated, univalent hydrocarbon groups on molecular terminal and that also contains an acrylic or methacrylic group and a silicon-bonded hydrolyzable group has not been known.
On the other hand, as disclosed in Kokai 2000-256558 and 2001-139815, in order to obtain a thermally conductive silicone composition with a large amount of thermally conductive filler, it is proposed to use as a surface-treating agent for the thermally conductive filler an organopolysiloxane with silicon-bonded hydrolyzable groups. However, when such an organopolysiloxane is used with large amounts of such thermally conductive fillers as alumina, the viscosity of the obtained silicone composition rapidly increases and makes the composition difficult for handling and forming.
Furthermore, Kokai 2003-213133 discloses the use of a surface-treating agent for thermally conductive filler in the form of an organopolysiloxane that contains vinyl groups and silicon-bonded hydrolyzable groups. Such an organopolysiloxane can be used in conjunction with large amounts of thermally conductive fillers such as alumina, but the problem is that the obtained silicone composition either does not possess thixotropy and easily precipitates during long storage, or becomes flowable during use.
It is an object of the present invention to provide a novel organopolysiloxane that contains on its terminals aliphatic, unsaturated, univalent hydrocarbon groups, an acrylic or methacrylic group, and silicon-bonded hydrolyzable groups. It is another object to provide a silicone composition that contains the aforementioned organopolysiloxane as a main component or as a surface-treating agent for a thermally conductive filler for obtaining a silicone composition of high thermal conductivity that is easy to handle and possesses appropriate thixotropy, even when the aforementioned thermally conductive filler is used in a large amount.